Asymmetric ruthenium tricarbonyl cyclopentadienone complexes; synthesis and application to asymmetric hydrogenation of ketones

A series of enantiomerically-pure ruthenium tricarbonyl cyclopentadienone complexes were prepared via the cyclisation of C2-symmetric dialkynes with Ru3(CO)12. Four complexes were characterised by X-ray crystallography and a hydride derivative of one of these was characterised. The complexes were tested in the asymmetric hydrogenation and transfer hydrogenation of acetophenone. Whilst the catalysts were active, acetophenone was reduced in low ee, however a reduction product of up to 46% ee could be obtained when a mild base (iPr2NEt or pyridine) was added to the reaction.